As ink leaves the reservoir chamber of an inkjet pen, such as when the pen is being used for a print job, or due to evaporation or printhead servicing, air can accumulate in the chamber to replace lost volume. The loss of ink from a printhead and the accompanying accumulation of air can lead to several printhead quality problems that may degrade the quality of the print job. These problems include changes in back pressure in the chamber as a result of environmental changes, and nozzle de-priming. With disposable pen sets, most of the problems associated with loss of ink from the printhead are manageable since the pen is discarded or recycled rather than being maintained for the life of the printer. However, many printers and other hardcopy devices utilize permanent pen sets. Permanent pen sets rely upon an ink supply reservoir fluidly connected to the pen to replenish ink as it is expelled through the printhead. But even when ink supply reservoirs are used, air accumulation is a concern since the quality of the printhead must be maintained throughout the life of the printer, and exposure of the ink to air can have an adverse impact on the ink and therefore the printhead.
Inkjet pens require regular servicing in order to maintain the pens and the quality of print jobs. This is especially true of printers and other hard copy apparatus that use permanent pen sets. Although there are many types of servicing systems and service stations, printhead servicing does not address the problems associated with accumulation of air inside the ink reservoir.
A pen having a printhead and a chamber for holding ink; a sensor for monitoring changes in the amount of ink in the chamber; and a pump for selectively drawing ink into or expelling ink from the chamber.